The present invention generally relates to a method of purifying water by filtration. More specifically, it relates to an improved water purification method in which influent water passes through a floc deck upstream of a filter bed.
Considerable developments have been made in improving the efficiency of systems for separating solids from liquids. In order to minimize the processing time and amounts of chemical agents needed for purification, it is important that a system be designed to operate as efficiently as possible.
One method of improving the efficiency of solids separation involves the formation of a zone of fluidized solids within a chamber through which influent water is passed. The zone of fluidized solids is derived from previously collected solid materials. For example, U.S. Pat. No. 1,893,451 to Smith involves the treatment of water with flocculating chemicals in a flocculation tank. The tank is designed so that water flows through zones of high turbidity prior to sedimentation. The zones of high turbidity allow newly formed floc particles to come into contact with previously formed floc particles, thereby stimulating the floc growth process and removal of contaminants.
U.S. Pat. No. 2,128,393 to Allen discloses a system consisting of flocculation and clarification chambers in series. Specifically, influent water is first combined with a flocculating chemical in the flocculation chamber to produce a fluid-solid suspension which subsequently passes into the clarification chamber. The suspension in the claification chamber is said to have a filtering action on influent liquid.
U.S. Pat. No. 2,382,490 to Lawlor involves a method and apparatus for treating water in which water is initially contacted with a precipitating agent. Thereafter, a coagulant is added to the water and the mixture is routed into a settling tank. The settling tank has an agitator which causes the mixture to form a blanket of sludge in the tank. Thereafter, water is routed upward through the settling tank and sludge blanket to accomplish filtration.
U.S. Pat. No. 3,587,861 to Ross discloses a filter bed of sand-type media on which a layer of solid waste materials collects during normal filtration. The layer is periodically agitated to form a suspension through which water can pass. The agitation, which is provided through mechanical means and can be assisted by the introduction of diffused air, is said to increase the filtering action of the total installation. Related technology is disclosed in U.S. Pat. Nos. 3,840,112; 3,516,930; 3,792,773; 3,817,378; 4,032,443 and Re. 28,458, all to Ross.
U.S. Pat. No. 4,608,181 discloses a particularly effective two stage filtration apparatus which does not employ a sludge blanket to enhance solids separation.
The present invention involves a method for enhancing the filtration capacity of such a multi-bed filter system in a substantially different manner from the above-described methods. The invention is characterized by improved filtration capacity, efficiency and economy.